1. Field of the Invention
The present invention relates generally to a device for bending pipe, and more particularly to an efficient, highly portable, pipe bending machine using an improved bending mandrel which may be used on various sizes of pipe but especially adaptable for pipe used in pipelines which transport oil and gas. The invention includes an improved mandrel which may be used to handle or shape pipe. When installing large diameter oil and gas pipelines it is often necessary to bend sections of the pipe to conform to abrupt changes in the terrain such as riverbeds or valleys. In order to make such bends, it has been found necessary to internally support the pipe during the bending operation in order to prevent deformation. Without proper internal support, the pipe wall along the outside of the bend will not expand as it should and the wall along the inside of the bend will be wrinkled or crimped. Such deformations are undesirable because it is often necessary for pipeline operators to force circular objects called "pigs" through the pipe to clear out the pipeline or separate various fluids flowing in the line. To accomplish this the pigs often have a diameter slightly greater than the pipe diameter thereby forming a seal as the pig moves along the pipe. If the pipe does not have a uniform circular cross-section over the length of the bend, the pig can become lodged within the pipe causing the entire pipeline to be shut down. Removal of such a lodged pig can be very expensive and time consuming.
In recent years the pipe used in construction of petroleum pipelines has drastically decreased in wall thickness. This use of relatively thin wall pipe has compounded the distortion problems previously experienced during bending.
Also, since the mandrel is placed inside the pipe to be bent, it has often been difficult to accurately position the mandrel.
2. Description of the Prior Art
The internal support needed to prevent pipe deformation during bending has in the past been provided by an internal pipe bending mandrel. This mandrel is placed inside the pipe and then expanded sufficiently to exert very high forces on the pipe wall in order to prevent distortion during bending.
The prior art as exemplified by U.S. Pat. Nos. 3,747,394; 3,964,290; 4,027,522 and 4,146,135 is generally illustrative of various internal mandrels. While such devices are generally acceptable for their intended purpose, they have not proven to be entirely satisfactory in preventing distortion and especially for use with relatively thin wall pipe.
U.S. Pat. No. 3,747,394 to Cunningham is representative of the pipe mandrels used in the past. This device uses a series of toggle joints securely connected to a central control device to clamp pipe engaging shoes in place against the internal portions of the pipe. Many such prior art devices have been unsuccessful in expanding the various toggle devices simultaneously and equally thereby causing unequal forces to be applied to the pipe. These unequal forces tend to increase the possibility of pipe deformation such as wrinkles and crimps. For example, the prior art has often used a lug and pin or bolt mechanism to secure the toggle joint to a common control such as the push-pull bar of Cunningham. Since it is necessary that such pins rotate within the lugs in order to create the toggle action, there exists some clearance space surrounding each pin. It has been found that, for example, in a device of the type disclosed in U.S. Pat. No. 3,747,394, this clearance space in each toggle joint causes a wave like movement of the shoes as the mandrel is expanded. This unequal application of the force from the shoes is particularly troublesome when thin walled pipe is bent. Often wrinkles and crimps result from such bends. Also, this problem of non-simultaneous movement of the pressure applying shoes is often compounded after the mandrel has been used for an extended period of time. After some use, components of many of the prior art devices have become worn or bent and therefore may fail to function properly.
Another problem which has persisted in the industry deals with non-aligned bends. The bending operation itself is typically performed by actually bending a small section of the pipe such as one or two feet then advancing the machine with respect to the pipe and the adjacent section is bent. However, it has often been a problem that the pipe is allowed to rotate or twist a small amount between each such bending operations. As a result of this twisting between the incremental bends, the entire section of pipe may be bent in a non-aligned or skewed manner.
As a result of the shortcomings of the prior art typified by the above, there has developed and continues to exist a substantial need for a pipe bending machine which can be used with relatively thin wall pipe while providing sufficient and yet uniformly applied internal support in order to prevent pipe distortion and skew during bending. Despite this need, and the efforts of many individuals and companies to develop such a device, a simple, compact machine which includes a mandrel capable of being accurately positioned and uniformly applying internal support to a pipe has heretofore been unavailable.
The problems enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of previously known pipe bending machine and mandrels. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that mandrels appearing in the art have not been altogether satisfactory.